It is well-known in the glass art to coat glass sheets with metallic and/or dielectric materials, to impart enhanced solar and optical properties to the glass sheets. For example, it is known to place multiple layers of metals and dielectrics onto glass to produce electrically conductive coatings which are transparent to visible light and highly reflective to infrared radiation. It is also known to deposit conductive metal oxides onto glass, such as, for example, fluorine-doped tin oxide, which oxides are also highly reflective to infrared radiation.
The transmitted and reflected colors of glass sheet coatings may also be varied, depending upon the thicknesses and optical interference effects of such coatings, the presence of color producing adjuvants, the color of the metal or dielectric layer deposited onto the glass, etc.
Many methods for depositing metal and dielectric coatings onto glass are well-known. Examples of conventional deposition processes include liquid and powder spray pyrolysis, wherein liquids or solid particles containing film forming reactants are sprayed onto the surface of a hot glass ribbon being produced by the well-known float glass process. A convenient method for depositing coatings onto glass is by way of chemical vapor deposition, wherein vaporized film-forming precursors are reacted at or near the surface of a hot glass ribbon to form the metal or dielectric film thereon. Chemical vapor deposition does not suffer from the problems associated with either liquid or powder spray pyrolysis processes. Liquid spray pyrolysis substantially cools the hot glass ribbon, while powder spray pyrolysis requires a complex, delicate powder handling and delivery system.
W. L. Jolly, "The Principles of Inorganic Chemistry," McGraw-Hill, New York (1976) p. 226 discloses that fluorine-doped tungstic oxide may be prepared from WO.sub.3 by replacing some of the oxygen atoms with fluorine atoms. Fluorine-doped tungstic oxide is blue in color, and its intensity is dependent upon the concentration of fluorine atoms in the matrix. Tungstic oxide additionally is electrically conductive and infrared energy reflective. A layer of fluorine-doped tungstic oxide on glass would be useful for producing a tinted, electrically heatable, solar load reducing glazing for automotive or architectural use.
A. W. Sleight, "Tungsten and Molybdenum Oxyfluorides of the Type MO.sub.3-x F.sub.x," Inorganic Chemistry, vol. 8, no. 8, (1969) pp. 1764-1767 discloses an alternative method for producing fluorine-doped tungstic oxide. Tungsten metal, tungstic oxide, and hydrofluoric acid are reacted together at about 700.degree. C. and 3,000 atmospheres to form single crystals of WO.sub.3-x F.sub.x, wherein x is from about 0.17 to about 0.66.
Also, C. E. Derrington et. al., "Preparation and Photoelectrolytic Behavior of the Systems WO.sub.3 and WO.sub.3-x F.sub.x," Inorganic Chemistry, vol. 17, no. 4 (1978) pp. 977-980 discloses a method for preparing fluorine-doped tungstic oxide, wherein tungstic oxide is reacted with potassium bifluoride at about 650.degree. C. to produce WO.sub.3-x F.sub.x.
Finally, D. K. Benson et al., "Preparation of Electrochromic Metal Oxide Films by Plasma-Enhanced Chemical Vapor Deposition," 31st Annual SPIE International Technical Symposium on Optics and Electro-Optics, Conference 823, August (1987) discloses the result of reacting together tungsten hexafluoride and oxygen in a plasma reactor. Tungstic oxide is formed, but without the inclusion of fluorine atoms. The article additionally discloses that the reaction between tungsten hexafluoride, molybdenum hexafluoride, and oxygen produces an oxide having two distinct phases; the first is fluorine-free tungstic oxide, and the second is MoO.sub.3-x F.sub.x. These results are surprising, since one would expect that the fluorine made available by the decomposition of the tungsten hexafluoride and molybdenum hexafluoride would result in fluorine doping of the tungstic oxide matrix as well as the molybedenum oxide matrix. However, only fluorine-free tungstic oxide was produced. Furthermore, the article does not suggest that the use of a fluorine-containing compound in addition to the disclosed compounds used in both reactions would be any more effective for doping the tungstic oxide than the available fluorine atoms generated by the decomposition of the tungsten hexafluoride reactant.
It must be noted that the prior art referred to hereinabove has been collected and examined only in light of the present invention as a guide. It is not to be inferred that such diverse art would otherwise be assembled absent the motivation provided by the present invention, nor that the cited prior art when considered in combination suggests the present invention absent the teachings herein.
It would be desirable to prepare fluorine-doped tungstic oxide by a simple chemical vapor deposition process, for coating glass surfaces for the production of blue tinted, electrically conductive, infrared radiation reflective automotive and architectural glazings.